Christa  Stehr

Christa Stehr

1618027905

Anatomy of a PostgreSQL Query Plan

The first thing to look at to start optimizing a query is the Query Planner. In this post we will explain how a query gets executed and how to understand the EXPLAIN command.

Introduction

Understanding the PostgreSQL query plan is a critical skill set for developers and database administrators alike. It is probably the first thing we would look at to start optimizing a query, and also the first thing to verify and validate if our optimized query is indeed optimized the way we expect it to be.

The query life cycle in PostgreSQL Database

Before we attempt to read a query plan it is important to ask some very basic questions:

  • Why do we even need a query plan?
  • What exactly is represented in the plan?
  • Is PostgreSQL not smart enough to optimize my queries automatically? Why should I worry about the planner?
  • Is the planner the only thing I need to look at?

#sql #databases #postgresql

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Anatomy of a PostgreSQL Query Plan
Ahebwe  Oscar

Ahebwe Oscar

1620185280

How model queries work in Django

How model queries work in Django

Welcome to my blog, hey everyone in this article we are going to be working with queries in Django so for any web app that you build your going to want to write a query so you can retrieve information from your database so in this article I’ll be showing you all the different ways that you can write queries and it should cover about 90% of the cases that you’ll have when you’re writing your code the other 10% depend on your specific use case you may have to get more complicated but for the most part what I cover in this article should be able to help you so let’s start with the model that I have I’ve already created it.

**Read More : **How to make Chatbot in Python.

Read More : Django Admin Full Customization step by step

let’s just get into this diagram that I made so in here:

django queries aboutDescribe each parameter in Django querset

we’re making a simple query for the myModel table so we want to pull out all the information in the database so we have this variable which is gonna hold a return value and we have our myModel models so this is simply the myModel model name so whatever you named your model just make sure you specify that and we’re gonna access the objects attribute once we get that object’s attribute we can simply use the all method and this will return all the information in the database so we’re gonna start with all and then we will go into getting single items filtering that data and go to our command prompt.

Here and we’ll actually start making our queries from here to do this let’s just go ahead and run** Python manage.py shell** and I am in my project file so make sure you’re in there when you start and what this does is it gives us an interactive shell to actually start working with our data so this is a lot like the Python shell but because we did manage.py it allows us to do things a Django way and actually query our database now open up the command prompt and let’s go ahead and start making our first queries.

#django #django model queries #django orm #django queries #django query #model django query #model query #query with django

Christa  Stehr

Christa Stehr

1618027905

Anatomy of a PostgreSQL Query Plan

The first thing to look at to start optimizing a query is the Query Planner. In this post we will explain how a query gets executed and how to understand the EXPLAIN command.

Introduction

Understanding the PostgreSQL query plan is a critical skill set for developers and database administrators alike. It is probably the first thing we would look at to start optimizing a query, and also the first thing to verify and validate if our optimized query is indeed optimized the way we expect it to be.

The query life cycle in PostgreSQL Database

Before we attempt to read a query plan it is important to ask some very basic questions:

  • Why do we even need a query plan?
  • What exactly is represented in the plan?
  • Is PostgreSQL not smart enough to optimize my queries automatically? Why should I worry about the planner?
  • Is the planner the only thing I need to look at?

#sql #databases #postgresql

Einar  Hintz

Einar Hintz

1619170861

Anatomy of a PostgreSQL Query Plan

Introduction

Understanding the PostgreSQL query plan is a critical skill set for developers and database administrators alike. It is probably the first thing we would look at to start optimizing a query, and also the first thing to verify and validate if our optimized query is indeed optimized the way we expect it to be.

The Query Life Cycle in PostgreSQL Database

Before we attempt to read a query plan it is important to ask some very basic questions:

  • Why do we even need a query plan?
  • What exactly is represented in the plan?
  • Is PostgreSQL not smart enough to optimize my queries automatically? Why should I worry about the planner?
  • Is the planner the only thing I need to look at?

Every query goes through different stages and it is important to understand what each stage means to the database.

PostgreSQL Query Lifecycle Diagram

Diagram of the PostgreSQL Query Lifecycle, made with https://app.diagrams.net/

The first phase is connecting to the database through either JDBC/ODBC (APIs created by Microsoft and Oracle, respectively, for interacting with databases) or by other means such as PSQL (a Terminal front-end for Postgres).

The second phase would be to translate the query to an intermediate format known as the parse tree. Discussing the internals of the parse tree would be beyond the scope of this article, but you can imagine it is like a compiled form of an SQL query.

The third phase is what we call the re-write system/rule system. It takes the parse tree generated from the second stage and re-writes it in a way that the planner/optimizer can start working in it.

The fourth phase is the most important phase and the heart of the database. Without the planner, the executor would be flying blind for how to execute the query, what indexes to use, whether to scan a smaller table to eliminate more unnecessary rows, etc. This phase is what we will be discussing in this article.

The fifth and final phase is the executor, which does the actual execution and returns the result. Almost all database systems follow a process that is more or less similar to the above.

#database #sql #postgresql #postgres

Raleigh  Hayes

Raleigh Hayes

1626922680

React Query Tutorial | React Query For Beginners

Hey everyone! Today’s video is a short tutorial for React Query, I’ve been using it for a few months now and it’s been great! Would definitely recommend checking it out.

Useful Links:
GitHub: https://github.com/redhwannacef/youtube/tree/master/react-query

#react query tutorial #react #query #react query

Charity  Ferry

Charity Ferry

1622793334

Useful PostgreSQL Commands/Queries

From the above output, we can also determine if the auto vacuum is running properly or not i.e… When the last auto vacuum ran on any particular table whose dead tuples are high.

Over time, due to MVCC, your table will grow in size (called table bloat)—this is why regular VACUUM is needed. This query will show you a list of tables and indexes with the most bloats. The value represents the number of “wasted bytes," or the difference between what is actually used by the table and index, and what we compute that it should be.

The way it works is it estimates the optimized size of the table/index by a calculation from each row sizes times total rows and compares that against the actual table size. Do note that this is an estimate, not an actual figure.

#postgresql #query